SOI substrate and manufacturing method thereof

ABSTRACT

An object is to provide an SOI substrate provided with a semiconductor layer which can be used practically even when a glass substrate is used as a base substrate. Another object is to provide a semiconductor device having high reliability using such an SOI substrate. An altered layer is formed on at least one surface of a glass substrate used as a base substrate of an SOI substrate to form the SOI substrate. The altered layer is formed on at least the one surface of the glass substrate by cleaning the glass substrate with solution including hydrochloric acid, sulfuric acid or nitric acid. The altered layer has a higher proportion of silicon oxide in its composition and a lower density than the glass substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an SOI (silicon on insulator) substrateand a manufacturing method thereof. Further, the present inventionrelates to a semiconductor device formed using the SOI substrate and amanufacturing method thereof.

2. Description of the Related Art

In recent years, integrated circuits using an SOI (silicon on insulator)substrate in which a thin single crystal semiconductor layer is providedover an insulating surface instead of a bulk silicon wafer have beendeveloped. Transistors in an integrated circuit can be formed so as tobe completely separated from each other by making the most ofcharacteristics of a thin single crystal silicon film formed over aninsulating surface. Further, since the transistors can be formed asfully depleted transistors, a semiconductor integrated circuit havinghigh added value such as high integration, high-speed driving, and lowpower consumption can be realized.

One of methods for manufacturing SOI substrates is a Smart Cut(registered trademark) method. By a Smart Cut method, not only an SOIsubstrate in which a single crystal silicon film is formed over asilicon substrate but also an SOI substrate in which a single crystalsilicon film is formed over an insulating substrate such as a glasssubstrate can be manufactured (for example, see Patent Document 1). Theoutline of the method for manufacturing an SOI substrate in which a thinsingle crystal silicon film is formed over a glass substrate using aSmart Cut method is as follows. First, a silicon dioxide film is formedover one surface of a piece of single crystal silicon. Next, hydrogenions are added to the piece of single crystal silicon, whereby ahydrogen-ion-introduced layer is formed at a predetermined depth of thepiece of single crystal silicon. Then, the piece of single crystalsilicon to which hydrogen ions are added is bonded to a glass substratewith the silicon dioxide film interposed therebetween. After that, heattreatment is performed, whereby the hydrogen-ion-introduced layerfunctions as a cleavage plane and then the piece of single crystalsilicon to which hydrogen ions are added is thinly separated. In thismanner, a thin single crystal silicon film can be formed over the glasssubstrate to which the piece of single crystal silicon is bonded. ASmart Cut (registered trademark) method may be referred to as ahydrogen-ion-implantation-separation method.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2004-87606.

SUMMARY OF THE INVENTION

The price per unit area of a glass substrate is low as compared withthat of a silicon substrate. Therefore, by using a glass substrate as abase substrate instead of a silicon substrate, an inexpensivelarge-sized SOI substrate can be manufactured. However, in themanufacturing process of an SOI substrate, if a foreign material existson any of surfaces of the glass substrate and the semiconductorsubstrate (the piece of single crystal silicon) when bonding of theglass substrate and the semiconductor substrate is performed, thebonding thereof is not performed at the periphery of the foreignmaterial. Then, when heat treatment is performed at this condition andthe semiconductor substrate is thinly separated, a semiconductor layer(a thin single crystal silicon film) is not formed at the periphery ofthe foreign material on the glass substrate, thereby generating adeficiency region in the semiconductor layer. In this manner, when anSOI substrate is manufactured using an glass substrate, there is aproblem in that a foreign material is interposed between a semiconductorsubstrate and the glass substrate and then a deficiency region of thesemiconductor layer of the SOI substrate is generated. When asemiconductor element is manufactured using the SOI substrate includingthe deficiency region in the semiconductor layer, the deficiency regionof the semiconductor layer may cause abnormality of variouscharacteristics of the semiconductor element. Further, in the process ofmanufacturing the SOI substrate using the glass substrate, thesemiconductor layer and a gate insulating film are at risk of beingcontaminated by movable ions such as alkali metal and alkaline earthmetal.

In view of the aforementioned problems, an object of an embodiment ofthe present invention is to provide an SOI substrate provided with asemiconductor layer which can be used practically even when a glasssubstrate is used for a base substrate and a manufacturing methodthereof. Further, another object of the present invention is to providea semiconductor device having high reliability using such an SOIsubstrate.

In an embodiment of the present invention, in order to solve theaforementioned problems, an altered layer is formed on at least onesurface of the glass substrate used as the base substrate of the SOIsubstrate to form the SOI substrate. The altered layer is formed on thesurface of the glass substrate by processing the glass substrate with asolution including hydrochloric acid, sulfuric acid or nitric acid. Thealtered layer has a higher proportion of silicon oxide in itscomposition and a lower density than the glass substrate.

An embodiment of the present invention is an SOI substrate including: aglass substrate having at least one surface on which an altered layer isformed; a first insulating layer provided over and in contact with thealtered layer; and a single crystal semiconductor layer provided overand in contact with the first insulating layer, and the altered layerhas a higher proportion of silicon oxide in its composition and a lowerdensity than the glass substrate.

Another embodiment of the present invention is an SOI substrateincluding: a glass substrate having at least one surface on which analtered layer is formed; a nitrogen-containing layer provided over andin contact with the altered layer; a first insulating layer providedover and in contact with the nitrogen-containing layer; and a singlecrystal semiconductor layer provided over and in contact with the firstinsulating layer, and the altered layer has a higher proportion ofsilicon oxide in its composition and a lower density than the glasssubstrate.

Another embodiment of the present invention is an SOI substrateincluding: a glass substrate having at least one surface on which analtered layer is formed; a second insulating layer provided over and incontact with the altered layer; a nitrogen-containing layer providedover and in contact with the second insulating layer; a first insulatinglayer provided over and in contact with the nitrogen-containing layer;and a single crystal semiconductor layer provided over and in contactwith the first insulating layer, and the altered layer has a higherproportion of silicon oxide in its composition and a lower density thanthe glass substrate.

Further, the concentrations of alkali metal and alkaline earth metal inthe altered layer are preferably lower than those in the glasssubstrate. In addition, between the glass substrate and the alteredlayer, an intermediate layer having values of the composition and thedensity of the intermediate layer which are intermediate between valuesof the glass substrate and the altered layer may be formed.

Note that each of the first insulating layer and the second insulatinglayer is preferably formed using a silicon oxide film. The silicon oxidefilm may be formed by a chemical vapor deposition method using anorganosilane gas. In addition, a chlorine atom may be included in thesilicon oxide film. Further, the nitrogen-containing layer is preferablyformed using a single layer or a stacked layer of a plurality of filmsselected from a silicon nitride film, a silicon nitride oxide film, anda silicon oxynitride film. Moreover, the glass substrate is preferablyformed from aluminosilicate glass, aluminoborosilicate glass or bariumborosilicate glass.

Another embodiment of the present invention is a manufacturing method ofan SOI substrate which is formed as follows: a glass substrate isprocessed with a solution including hydrochloric acid, sulfuric acid ornitric acid to form an altered layer on at least one surface of theglass substrate; a single crystal semiconductor substrate is bonded tothe altered layer with a first insulating layer interposed therebetween;part of the single crystal semiconductor substrate is separated to forma single crystal semiconductor layer over the glass substrate.

Another embodiment of the present invention is a manufacturing method ofan SOI substrate which is formed as follows: a glass substrate isprocessed with a solution including hydrochloric acid, sulfuric acid ornitric acid; an altered layer is formed on at least one surface of theglass substrate; a single crystal semiconductor substrate is bonded tothe altered layer with a nitrogen-containing layer and a firstinsulating layer interposed therebetween; and part of the single crystalsemiconductor substrate is separated to form a single crystalsemiconductor layer over the glass substrate.

Another embodiment of the present invention is a manufacturing method ofan SOI substrate which is formed as follows: a glass substrate isprocessed with a solution including chlorine, sulfuric acid or nitricacid; an altered layer is formed on at least one surface of the glasssubstrate; a single crystal semiconductor substrate is bonded to thealtered layer with a second insulating layer, a nitrogen-containinglayer and a first insulating layer interposed therebetween; and part ofthe single crystal semiconductor substrate is separated to form a singlecrystal semiconductor layer over the glass substrate.

Note that a hydrochloric acid/hydrogen peroxide solution mixture whichis formed by mixing hydrochloric acid, hydrogen peroxide solution andpure water is preferably used as the solution including hydrochloricacid, sulfuric acid or nitric acid. In addition, ultrasonic oscillationis preferably applied to the solution including hydrochloric acid,sulfuric acid or nitric acid in the above treatment.

Note that in this specification, the altered layer is formed on at leastone surface of a glass substrate and has a higher proportion of siliconoxide in its composition and a lower density than the glass substrate.The proportion of the silicon oxide is judged by a peak and a chemicalshift of a photoelectron spectrum measured with the use of X-rayphotoelectron spectroscopy (XPS). Further, the density is judged bychecking results from X-ray reflectivity (XRR) measurement withsimulation results.

Note that a semiconductor device in this specification generallyindicates a device capable of functioning by utilizing semiconductorcharacteristics, and electro-optical devices, semiconductor circuits,and electronic apparatuses are all semiconductor devices.

In addition, in this specification, a display device includes alight-emitting device and a liquid crystal display device. Thelight-emitting device includes a light-emitting element, and the liquidcrystal display device includes a liquid crystal element. Thelight-emitting element includes, in its category, an element whoseluminance is controlled by current or a voltage, and specificallyincludes an inorganic electroluminescent (EL) element, an organic ELelement, and the like.

According to an embodiment of the present invention, an SOI substrateprovided with the semiconductor layer which can be used practically canbe provided even when a glass substrate is used as a base substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C each illustrate an SOI substrate according to anembodiment of the present invention.

FIGS. 2A and 2B each illustrate an SOI substrate according to anembodiment of the present invention.

FIGS. 3A and 3B illustrate methods for manufacturing an SOI substrateaccording to an embodiment of the present invention.

FIGS. 4A and 4B illustrate a method for manufacturing an SOI substrateaccording to an embodiment of the present invention.

FIGS. 5A to 5D illustrate a method for manufacturing an SOI substrateaccording to an embodiment of the present invention.

FIGS. 6A and 6B illustrate a method for manufacturing an SOI substrateaccording to an embodiment of the present invention.

FIGS. 7A to 7D illustrate a method for manufacturing a semiconductordevice using an SOI substrate according to an embodiment of the presentinvention.

FIGS. 8A to 8C illustrate a method for manufacturing a semiconductordevice using an SOI substrate according to an embodiment of the presentinvention.

FIG. 9 is a diagram showing a semiconductor device using an SOIsubstrate according to an embodiment of the present invention.

FIG. 10 is a diagram showing a semiconductor device using an SOIsubstrate according to an embodiment of the present invention.

FIG. 11 illustrates a display device using an SOI substrate according toan embodiment of the present invention.

FIGS. 12A and 12B illustrate a display device using an SOI substrateaccording to an embodiment of the present invention.

FIGS. 13A and 13B illustrate a display device using an SOI substrateaccording to an embodiment of the present invention.

FIGS. 14A to 14C each illustrate an electronic appliance in which an SOIsubstrate according to an embodiment of the present invention is used.

FIGS. 15A and 15B are STEM images of a glass substrate according to anexample of the present invention.

FIG. 16 is a graph of photoelectron spectroscopy spectrum by XPS of aglass substrate according to an example of the present invention.

FIG. 17 is a graph of photoelectron spectroscopy spectrum by XPS of aglass substrate according to an example of the present invention.

FIG. 18 is a graph of a deficiency region in a semiconductor layer of anSOI substrate according to an embodiment of the present invention.

Hereinafter, embodiments and examples of the present invention will bedescribed with reference to the drawings. However, the present inventioncan be implemented in various different modes, and it is to be easilyunderstood that various changes and modifications in modes and detailsthereof will be apparent to those skilled in the art without departingfrom the meaning and the scope of the present invention. Therefore, thisinvention should not be interpreted as being limited to the descriptionof the embodiments. Through the drawings for illustrating embodiments,like components are denoted by like reference numerals and repetitivedescription thereof is not made.

Embodiment 1

In this embodiment, structures of an SOI substrate according to thepresent invention is described with reference to FIGS. 1A to 1C.

FIG. 1A illustrates an SOI substrate having a structure in which aninsulating layer 102 is formed over a glass substrate 110 having onesurface provided with an altered layer 111 and a semiconductor layer 122is formed over the insulating layer 102. Here, as the glass substrate110, a glass substrate selected from a variety of glass substrates thatare used in the electronics industry is preferably used, such as asubstrate of aluminosilicate glass, aluminoborosilicate glass, or bariumborosilicate glass. Further, as the glass substrate 110, a glasssubstrate having any of the following size can be used: 3rd generation(550 mm×650 mm); 3.5th generation (600 mm×720 mm or 620 mm×750 mm); 4thgeneration (680×880 mm or 730 mm×920 mm); 5th generation (1100 mm×1300mm); 6th generation (1500 mm×1850 mm); 7th generation (1870 mm×2200 mm);8th generation (2200×2400 mm); 9th generation (2400 mm×2800 mm or 2450mm×3050 mm); and 10th generation (2850 mm×3050 mm or 2950 mm×3400 mm).

The altered layer 111 is formed on the one surface of the glasssubstrate 110. Here, the altered layer 111 is formed on at least the onesurface of the glass substrate 110 and has a higher proportion ofsilicon oxide in its composition and a lower density than the glasssubstrate 110. In addition, the altered layer 111 has lowerconcentrations of alkali metal, alkaline earth metal and metal than theglass substrate 110. Here, the proportion of the silicon oxide is judgedby a peak and a chemical shift of a photoelectron spectrum measured withthe use of X-ray photoelectron spectroscopy (XPS). Further, the densityis judged by checking results from X-ray reflectivity (XRR) measurementwith simulation results. As for the composition of the altered layer111, silicon and oxygen preferably account for higher than or equal to90%, more preferably higher than or equal to 99% in the case of themeasurement with the use of XPS. Metal such as aluminum and calcium;boron; and alkaline earth metal such as strontium and magnesiumpreferably account for lower than or equal to 10%, more preferably lowerthan or equal to 1%. Moreover, the thickness of the altered layer 111 ispreferably greater than or equal to 5 nm and less than or equal to 3 μm.The altered layer 111 having such a thickness is preferable because thethickness of the altered layer 111 and the diameter of a foreignmaterial become almost the same. Further, the density of the alteredlayer 111 is preferably greater than or equal to 1.5 g/cm³ and less thanor equal to 2.5 g/cm³, in particular, greater than or equal to 1.8 g/cm³and less than or equal to 2.3 g/cm³. The altered layer 111 is preferablyformed by processing the glass substrate 110 with the use of a solutionincluding hydrochloric acid, sulfuric acid or nitric acid. Inparticular, the altered layer 111 is preferably formed by processing theglass substrate 110 with the use of a hydrochloric acid/hydrogenperoxide solution mixture (HPM) which is a mixed solution ofhydrochloric acid, a hydrogen peroxide solution and pure water. Notethat the altered layer 111 is not necessarily formed on only the onesurface of the glass substrate 110; for example, the altered layer 111may be formed on the entire surface of the glass substrate 110.

In addition, an intermediate layer having values of the composition andthe density which are intermediate between values of the glass substrate110 and the altered layer 111 may exist between the glass substrate 110and the altered layer 111.

Typically, single crystal silicon is applied to the semiconductor layer122. Alternatively, silicon which can be separated from apolycrystalline semiconductor substrate by ahydrogen-ion-implantation-separation method or germanium which can beseparated from a single crystal semiconductor substrate or apolycrystalline semiconductor substrate by ahydrogen-ion-implantation-separation method can be used. Stillalternatively, a crystalline semiconductor substrate of a compoundsemiconductor such as silicon germanium, gallium arsenide, or indiumphosphide can be used.

The insulating layer 102 is provided between the altered layer 111 andthe semiconductor layer 122. As the insulating layer 102, a smoothinsulating layer having a hydrophilic surface is preferable and asilicon oxide film is suitable. In particular, a silicon oxide filmformed by a chemical vapor deposition method using an organosilane gasis preferable. Examples of the organosilane gas includesilicon-containing compounds such as tetraethoxysilane (TEOS) (chemicalformula: Si(OC₂H₅)₄), tetramethylsilane (TMS) (chemical formula:Si(CH₃)₄), trimethylsilane (chemical formula: (CH₃)₃SiH),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (chemical formula:SiH(OC₂H₅)₃), and tris(dimethylamino)silane (chemical formula:SiH(N(CH₃)₂)₃). Note that a silicon oxynitride film may be used as theinsulating layer 102 instead of a silicon oxide film.

Further, an oxide film formed by thermally oxidizing the semiconductorlayer 122 may be used as the insulating layer 102. In addition, byinclusion of a chlorine atom in the oxide film, reduction of theinterface state of the insulating layer 102 and quality improvement ofthe oxide film can be realized. Furthermore, the oxide film which isformed by thermal oxidation is suitable for an insulating film of theSOI substrate because the number of particles in or on the oxide film isremarkably small. Further, by inclusion of a chlorine atom in the oxidefilm, a heavy metal which is an extrinsic impurity is captured so as toprevent contamination of the semiconductor layer. As the insulatinglayer 102, chemical oxide can also be used. Chemical oxide can be formedby, for example, treatment of a surface of a semiconductor substratethat is to become an SOI layer with ozone-containing water. Sincechemical oxide reflects the shape of the surface of the semiconductorsubstrate, it is preferable that the semiconductor substrate be flat sothat the chemical oxide also becomes flat.

The insulating layer 102 is formed to a thickness of greater than orequal to 5 nm and less than or equal to 500 nm. With this thickness, itis possible to smooth the surface roughness of a surface of theinsulating layer 102 (a surface on which bonding is performed) and alsoto ensure smoothness of a growth surface of the layer. Further, byprovision of the insulating layer 102, thermal distortion of the glasssubstrate 110 and the semiconductor layer 122 can be relieved. In otherwords, when the glass substrate 110 is bonded to the semiconductor layer122, the insulating layer 102 is provided over the surface of thesemiconductor layer 122 on which bonding is performed, whereby the glasssubstrate 110 and the semiconductor layer 122 can be bonded strongly.

FIG. 1B illustrates an SOI substrate having a structure in which anitrogen-containing layer 104, the insulating layer 102 and thesemiconductor layer 122 are provided over the glass substrate 110 havingthe one surface on which the altered layer 111 is formed. That is, FIG.1B illustrates the SOI substrate having a structure in which thenitrogen-containing layer 104 is added between the altered layer 111 andthe insulating layer 102 of the structure in FIG. 1A. Here, thenitrogen-containing layer 104 is a film containing at least nitrogen andsilicon. Provision of the nitrogen-containing layer 104 between thealtered layer 111 and the insulating layer 102 prevents thesemiconductor layer 122 from being contaminated by impurities diffusedfrom the glass substrate 110 such as movable ions of, for example,alkali metal or alkaline earth metal, moisture or the like. Thenitrogen-containing layer 104 is preferably formed using a single layeror a stacked layer of a plurality of films selected from a siliconnitride film, a silicon nitride oxide film, and a silicon oxynitridefilm.

Note that a silicon oxynitride film refers to a film which contains moreoxygen than nitrogen and, in the case where measurements are performedusing Rutherford backscattering spectrometry (RBS) and hydrogen forwardscattering (HFS), contains oxygen, nitrogen, silicon, and hydrogen atconcentrations of greater than or equal to 50 and less than or equal to70 at. %, greater than or equal to 0.5 and less than or equal to 15 at.%, greater than or equal to 25 and less than or equal to 35 at. %, andgreater than or equal to 0.1 and less than or equal to 10 at. %,respectively. Further, a silicon nitride oxide film refers to a filmthat contains more nitrogen than oxygen and, in the case wheremeasurements are performed using RBS and HFS, contains oxygen, nitrogen,silicon, and hydrogen at concentrations of greater than or equal to 5at. % and less than or equal to 30 at. %, greater than or equal to 20at. % and less than or equal to 55 at. %, greater than or equal to 25at. % and less than or equal to 35 at. %, and greater than or equal to10 at. % and less than or equal to 30 at. %, respectively. Note thatpercentages of nitrogen, oxygen, silicon, and hydrogen fall within theranges given above, where the total number of atoms contained in thesilicon oxynitride film or the silicon nitride oxide film is defined as100 at. %.

FIG. 1C illustrates the SOI substrate having a structure in which aninsulating layer 105, the nitrogen-containing layer 104, the insulatinglayer 102 and the semiconductor layer 122 are provided over the glasssubstrate 110 having the one surface on which the altered layer 111 isformed. That is, FIG. 1C illustrates the SOI substrate having astructure in which the insulating layer 105 is added between the alteredlayer 111 and the nitrogen-containing layer 104 of the structure in FIG.1B. The insulating layer 105 preferably has a smooth insulating layerhaving a hydrophilic surface, and a silicon oxide film is suitable. Inparticular, a silicon oxide film formed by a chemical vapor depositionmethod using an organosilane gas is preferable. Examples of anorganosilane gas include silicon-containing compounds such astetraethoxysilane (TEOS) (chemical formula: Si(OC₂H₅)₄),tetramethylsilane (chemical formula: Si(CH₃)₄), trimethylsilane(chemical formula: (CH₃)₃SiH), tetramethylcyclotetrasiloxane (TMCTS),octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS),triethoxysilane (chemical formula: SiH(OC₂H₅)₃), andtris(dimethylamino)silane (chemical formula: SiH(N(CH₃)₂)₃).

In this embodiment, since the altered layer 111 formed on at least theone surface of the glass substrate 110 has a high proportion of siliconoxide and a large amount of silicon oxide appears on the surface of thealtered layer 111 as compared to the glass substrate 110, a strongcovalent bond is likely to be formed in a bonding interface between thealtered layer 111 and the insulating layer 102, the nitrogen-containinglayer 104 or the insulating layer 105. Further, since the altered layer111 has a low density as compared to the glass substrate 110, theYoung's modulus of the altered layer 111 is small and therefore, thealtered layer 111 is easily deformed. Accordingly, when the insulatinglayer 102, the nitrogen-containing layer 104 or the insulating layer 105is bonded to the altered layer 111, even when a foreign material existson the surface of either the insulating layer 102, thenitrogen-containing layer 104 or the insulating layer 105, unevennessgenerated due to the foreign material can be reduced since the alteredlayer 111 is deformed. As compared to the case of bonding with the glasssubstrate 110 not provided with the altered layer 111, a region in aperiphery of the foreign material, in which bond is not formed, isreduced and the number of the regions is also reduced. Therefore, ascompared to the case where the insulating layer 102, thenitrogen-containing layer 104 or the insulating layer 105 is bonded tothe glass substrate 110, a deficiency region of the semiconductor layer122 of this embodiment is reduced and the number of the deficiencyregions is also reduced. In particular, it is preferable that thethickness of the altered layer 111 be greater than or equal to 5 nm andless than or equal to 3 μm because the thickness of the altered layer111 and the diameter of the foreign material are almost the same in thiscase.

Further, in the altered layer 111, impurities such as movable ions ofalkali metal and alkaline earth metal which contaminate thesemiconductor layer are reduced and thus contamination of thesemiconductor layer 122 can be reduced. In the SOI substrate having thestructure of FIG. 1A, the nitrogen-containing layer 104 functioning as ablocking layer does not exist; therefore, the altered layer 111 isparticularly effective. In the case where the plurality of semiconductorlayers 122 is bonded to the large glass substrate 110 without the layerfunctioning as a blocking layer, as illustrated in FIG. 2A, acontaminated region 130 contaminated by impurities such as movable ionsof alkali metal and alkaline earth metal is formed in the semiconductorlayer 122. In contrast, as illustrated in FIG. 2B, in the case where theplurality of semiconductor layers 122 is bonded to the large glasssubstrate 110 having one surface on which the altered layer 111 isformed, the semiconductor layer 122 is prevented from being contaminatedby impurities such as movable ions of alkali metal and alkaline earthmetal. Further, in a process through which a semiconductor device suchas a thin film transistor is formed using this SOI substrate, thesemiconductor layer 122 and a gate insulating film formed over thesemiconductor layer are prevented from being contaminated by impuritiessuch as movable ions of alkali metal and alkaline earth metal.

In this manner, although a glass substrate is used as a base substrateof an SOI substrate, the deficiency region of the semiconductor layercan be reduced and thus the SOI substrate provided with thesemiconductor layer which can be used practically can be provided.

Embodiment 2

In this embodiment, a method for manufacturing an SOI substrateaccording to the present invention is described with reference to FIGS.3A and 3B, FIGS. 4A and 4B, FIGS. 5A to 5D and FIGS. 6A and 6B.

First, a glass substrate 110 is processed with the use of a solution 123including hydrochloric acid, sulfuric acid or nitric acid. Here, thesame glass substrate as the glass substrate described in Embodiment 1 isused for the glass substrate 110. The treatment is not necessarilyperformed on the entire surface of the glass substrate 110 and may beperformed so that at least a surface which is to be bonded to thesemiconductor layer 122 is processed. As the solution 123, for example,a hydrochloric acid/hydrogen peroxide solution mixture (HPM), which is amixed solution of hydrochloric acid, a hydrogen peroxide solution andpure water, or a sulfuric acid/hydrogen peroxide mixture (SPM), which isa mixed solution of sulfuric acid and a hydrogen peroxide solution, isused. Preferably, a hydrochloric acid/hydrogen peroxide solution mixture(HPM), which is a mixed solution of hydrochloric acid, a hydrogenperoxide solution and pure water, is used. More preferably, when thetreatment is performed using HPM, the temperature of the mixed solutionis raised to higher than or equal to 70° C. and lower than or equal to90° C.; when the treatment is performed using SPM, the temperature ofthe mixed solution is raised to higher than or equal to 80° C. and lowerthan or equal to 120° C. Further, when the solution 123 is processedwhile ultrasonic waves are applied thereto, the rest of abrasive(slurry) typified by cerium oxide and particles can be removed andreattachment thereof can be prevented. Further, after the treatment withthe solution 123, cleaning with pure water is preferably performed.Then, water droplets existing on the glass substrate 110 are preferablydried. By cleaning with pure water, the solution 123 attached to theglass substrate 110 can be removed.

For example, the glass substrate 110 can be processed with the use of abatch-type cleaning machine (see FIG. 3A). In the batch-type cleaningmachine, the treatment of the glass substrate 110 is performed asfollows. The glass substrate 110 is set in a carrier 125 fixed by atransport chuck 126 and the carrier 125 holding the glass substrate 110is soaked in a cleaning bath 124 filled with the solution 123. At thistime, the glass substrate 110 is preferably soaked in the solution 123for approximately 10 minutes. Further, by using an ultrasonic cleaningbath as the cleaning bath 124, ultrasonic cleaning can be performed withthe use of the solution 123 to which ultrasonic oscillation having afrequency of greater than or equal to 15 kHz and less than or equal to 1MHz, preferably greater than or equal to 30 kHz and less than or equalto 50 kHz is applied. Further, when a plurality of glass substrates 110is set in the carrier 125, the plurality of glass substrates 110 can beprocessed together by one treatment. Further, after the treatment withthe solution 123, it is preferable that the glass substrate 110 issoaked in a cleaning bath filled with pure water for approximately 10minutes and then dried with a rinser dryer so that water dropletsexisting on the glass substrate 110 are dried.

Further, the glass substrate 110 can also be processed with the use of asingle wafer cleaning machine (see FIG. 3B). In the single wafercleaning machine, the glass substrate 110 is processed as follows. Theglass substrate 110 is fixed to a mandrel 127 so as to be rotated andthen the solution 123 is supplied from a cleaning nozzle 128 on thesurface side. Further, megahertz ultrasonic cleaning (megasoniccleaning) can be performed by using a cleaning nozzle which vibrates thesolution 123 with the use of ultrasonic waves (megahertz ultrasonicwaves) having a frequency of greater than or equal to 700 kHz and lessthan or equal to 2 MHz, preferably greater than or equal to 800 kHz andless than or equal to 1 MHz as the cleaning nozzle 128. In addition, thecleaning nozzle 128 may be provided not only on the surface side butalso on a rear surface side of the glass substrate 110. Further,megasonic cleaning may be performed using a nozzle capable of supplyingpure water to which an ultrasonic oscillation having a frequency ofgreater than or equal to 700 kHz and less than or equal to 2 MHz,preferably greater than or equal to 800 kHz and less than or equal to 1MHz is applied in addition to the cleaning nozzle 128 supplying thesolution 123. Further, after the treatment with the solution 123, it ispreferable that the glass substrate 110 is cleaned with the use of thenozzle capable of supplying pure water and dried with a rinser dryer sothat water droplets existing on the glass substrate 110 are dried.

Alternatively, the glass substrate 110 can be disposed over a transportroller 129, whereby the glass substrate 110 may be processed while beingtransported (see FIG. 4A). The solution 123 is supplied to the glasssubstrate 110 is from the cleaning nozzle 128 over the glass substrate110 while the glass substrate 110 is transported by the transport roller129. Further, megasonic cleaning can be performed by using a cleaningnozzle which vibrates the solution 123 with the use of ultrasonic waveshaving a frequency of greater than or equal to 700 kHz and less than orequal to 2 MHz, preferably greater than or equal to 800 kHz and lessthan or equal to 1 MHz as the cleaning nozzle 128. Further, use of thetransport roller 129 facilitates treatment of a large-sized glasssubstrate. In addition, after the treatment with the solution 123, it ispreferable that the glass substrate 110 is cleaned with the use of thenozzle capable of supplying pure water and dried with a rinser dryer sothat water droplets existing on the glass substrate 110 are dried.

By the treatment described above, ions of alkali metal, alkaline earthmetal and metal are eluted from at least one surface of the glasssubstrate 110. Accordingly, the altered layer 111 which has a higherproportion of silicon oxide in its composition and a lower density thanthe glass substrate 110 is formed on at least the one surface of theglass substrate 110 (see FIG. 4B). In addition, liftoff and removal ofparticles and the like over the glass substrate 110 are performed at thesame time as the elution of metal. As for the composition of the alteredlayer 111, silicon and oxygen preferably account for higher than orequal to 90%; more preferably higher than or equal to than 99% in thecase of the measurement with the use of X-ray photoelectron spectroscopy(XPS). Metal, such as aluminum and calcium; boron; and alkaline earthmetal, such as strontium and magnesium preferably account for lower thanor equal 10%; more preferably, lower than or equal to 1%. Moreover, thethickness of the altered layer 111 is preferably greater than or equalto 5 nm and less than or equal to 3 p.m. Further, the density of thealtered layer 111 is preferably greater than or equal to 1.5 g/cm³ andless than or equal to 2.5 g/cm³; in particular, preferably greater thanor equal to 1.8 g/cm³ and less than or equal to 2.3 g/cm³. Note that thealtered layer 111 is formed on only the one surface of the glasssubstrate 110 in FIG. 4B; however, the present invention is not limitedthereto. For example, the altered layer 111 may be formed over theentire surface of the glass substrate 110.

As the glass substrate 110, a large-sized mother glass substratereferred to as the 6th generation (1500 mm×1850 mm), the 7th generation(1870 mm×2200 mm), the 8th generation (2200 mm×2400 mm), the 9thgeneration (2400 mm×2800 mm or 2450 mm×3050 mm), or the 10th generation(2850 mm×3050 or 2950 mm×3400 mm) can be used. A large-sized motherglass substrate is used as the glass substrate 110 and the glasssubstrate is bonded to a plurality of semiconductor substrates tomanufacture an SOI substrate, whereby the SOI substrate can have alarger size. Thus, the number of display panels which can bemanufactured from a single substrate (panels yielded per substrate) canbe increased, and accordingly, productivity can be improved.

Next, a semiconductor substrate 101 is prepared, and the insulatinglayer 102 and the nitrogen-containing layer 104 are formed over asurface of the semiconductor substrate 101 (see FIG. 5A).

As the semiconductor substrate 101, a commercial semiconductor substratecan be used; typically, a single crystal silicon substrate is used.Alternatively, silicon which can be separated from a polycrystallinesemiconductor substrate by a hydrogen-ion-implantation-separation methodor germanium which can be separated from a single crystal semiconductorsubstrate or a polycrystalline semiconductor substrate by ahydrogen-ion-implantation-separation method can be used. Stillalternatively, a crystalline semiconductor substrate of a compoundsemiconductor such as silicon germanium, gallium arsenide, or indiumphosphide can also be used. As the commercial single crystal siliconsubstrate, typically, a circular substrate which is 5 inches in diameter(125 mm), 6 inches in diameter (150 mm), 8 inches in diameter (200 mm),and 12 inches in diameter (300 mm). Note that the shape of the singlecrystal silicon substrate is not limited to a circular shape, and asingle crystal silicon substrate processed into a rectangular shape orthe like can also be used.

An insulating layer having a smooth surface is preferably used as theinsulating layer 102, and a silicon oxide film is suitable. Further, theinsulating layer 102 is preferably deposited to a thickness of greaterthan or equal to 5 nm and less than or equal to 500 nm.

In particular, a silicon oxide film which is deposited by a chemicalvapor deposition method using an organosilane gas is preferable. This isbecause the insulating layer 102 can have a flat surface by using thesilicon oxide film formed using an organosilane gas.

Examples of the organosilane gas include silicon-containing compoundssuch as tetraethoxysilane (TEOS) (chemical formula: Si(OC₂H₅)₄),tetramethylsilane (TMS) (chemical formula: Si(CH₃)₄), trimethylsilane(chemical formula: (CH₃)₃SiH), tetramethylcyclotetrasiloxane (TMCTS),octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS),triethoxysilane (chemical formula: SiH(OC₂H₅)₃), andtris(dimethylamino)silane (chemical formula: SiH(N(CH₃)₂)₃).

Here, a silicon oxide film which is deposited by a chemical vapordeposition method using organosilane as a source gas is formed over thesemiconductor substrate 101. Alternatively, a silicon oxide film or asilicon oxynitride film which is deposited by a chemical vapordeposition method using a silane as a source gas can be used.

Alternatively, as the insulating layer 102, an oxide film formed bythermally oxidizing the semiconductor substrate 101 may be used. Inaddition, thermal oxidation treatment may be performed on thesemiconductor substrate 101 in an oxidation atmosphere to which chlorineis added, whereby a chlorine atom may be included in the oxide film. Byinclusion of a chlorine atom in the insulating layer 102, reduction ofthe interface state of the insulating layer 102 and quality improvementof the oxide film can be realized. Further, by inclusion of a chlorineatom in the insulating layer 102, a heavy metal which is an extrinsicimpurity is captured so as to prevent contamination of the semiconductorlayer. As the insulating layer 102, chemical oxide can also be used.Chemical oxide can be formed by, for example, treatment of a surface ofa semiconductor substrate that is to become an SOI layer withozone-containing water. Since the chemical oxide reflects the shape ofthe surface of the semiconductor substrate, it is preferable that thesemiconductor substrate be flat so that the chemical oxide also becomesflat.

And then, the nitrogen-containing layer 104 is formed over theinsulating layer 102. When part of the semiconductor substrate 101 isbonded to the glass substrate to form the semiconductor layer 122, thenitrogen-containing layer 104 also functions as a barrier layer forpreventing impurities such as movable ions of alkali metal, alkalineearth metal, moisture and the like included in the glass substrate 110from being diffused to the semiconductor layer 122.

The nitrogen-containing layer 104 is a film which at least includesnitrogen and silicon. For example, the nitrogen-containing layer 104 isdeposited so as to have a single layer structure or a stacked layerstructure which includes any of a silicon nitride film, a siliconnitride oxide film, or a silicon oxynitride film by a CVD method or thelike. The nitrogen-containing layer 104 is formed in the range ofgreater than or equal to 10 nm and less than or equal to 200 nm;preferably in the range of greater than or equal to 50 nm and less thanor equal to 100 nm.

For example, a silicon nitride oxide film which is deposited by a plasmaCVD method at a low temperature (higher than or equal to 100° C. andlower than or equal to 350° C., preferably higher than or equal to 150°C. and lower than or equal to 300° C.) is suitable for thenitrogen-containing layer 104. A silicon nitride oxide film having asmooth surface can be obtained by depositing by a plasma CVD method at alow temperature. In addition, the deposition at a low temperature canprevent an embrittlement layer 103 formed in the semiconductor substrate101 from being degassed. Note that a heat treatment temperature forseparating the semiconductor layer 122 from the semiconductor substrate101 is higher than the deposition temperature of the nitrogen-containinglayer.

In this embodiment, the silicon oxide film having a smooth surface isprovided as the insulating layer 102, thereby flattening a surface ofthe nitrogen-containing layer 104 which is formed over the insulatinglayer 102. Note that in the case where the semiconductor substrate 101has a flat surface, a structure in which the insulating layer 102 is notprovided may be employed. For example, the nitrogen-containing layer 104can be formed of a single layer selected from a silicon oxynitride filmor a silicon nitride oxide film, or can be formed of a stack of asilicon oxynitride film and a silicon nitride oxide film which arestacked in this order from the semiconductor substrate 101 side.

Next, the semiconductor substrate 101 is irradiated with an ion beam 121including ions accelerated by an electric field through the insulatinglayer 102 and the nitrogen-containing layer 104, whereby theembrittlement layer 103 is formed in a region at a predetermined depthfrom the surface of the semiconductor substrate 101 (see FIG. 5B). Theion beam 121 is generated in such a manner that a source gas is excited,plasma of the source gas is generated, and ions included in the plasmaare extracted from the plasma by the action of an electric field.

The depth at which the embrittlement layer 103 is formed can be adjustedby the acceleration energy of the ion beam 121 and the angle at whichthe ion beam 121 enters. The acceleration energy can be adjusted by anacceleration voltage, dosage, or the like. The embrittlement layer 103is formed at the same depth or substantially the same depth as theaverage depth at which the ions have entered. The thickness of thesemiconductor layer 122 which is to be separated from the semiconductorsubstrate 101 is determined in accordance with the depth at which theions are added. The depth at which the embrittlement layer 103 is formedis greater than or equal to 10 nm and less than or equal to 500 nm fromthe surface of the semiconductor substrate 101; preferably, greater thanor equal to 50 nm and less than or equal to 200 nm from the surface ofthe semiconductor layer 101.

In order to add ions to the semiconductor substrate 101, anion-implantation method in which mass separation is performed may beemployed, or an ion-doping method in which mass separation is notperformed may be employed.

In the case of using hydrogen (H₂) for the source gas, the hydrogen gascan be excited to generate plasma including H⁺, H₂ ⁺, and H₃ ⁺. Theproportion of ion species generated from the source gas can be changedby adjusting a plasma-excitation method, pressure in an atmosphere forgenerating plasma, the amount of a source gas supplied, and the like.With respect to the total amount of H+, H₂+, and H₃+ included in the ionbeam 121, H₃ ⁺ is preferably included in the ion beam 121 at greaterthan or equal to 50%, and further preferably at greater than or equal to80%.

H₃ ⁺ ions includes more hydrogen atoms than other hydrogen ion species(H⁺ ions and H₂ ⁺ ions), and as a result, the mass of H₃ ⁺ ions islarge. Thus, in the case where H⁺ ions, H₂ ⁺ ions, and H₃ ⁺ ions areaccelerated by the same energy, H₃ ⁺ ions are added to a regionshallower than regions in the semiconductor substrate 101 where H⁺ ionsand H₂ ⁺ ions are added. Therefore, by a high proportion of H₃ ⁺included in the ion beam 121, variation in the average penetration depthof the hydrogen ions becomes small; accordingly, a concentration profileof hydrogen in a depth direction in the semiconductor substrate 101becomes steep, and a peak position of the profile can be made to beshallow. Consequently, it is preferable that H₃ is preferably includedin the ion beam 121 at greater than or equal to 50%, and furtherpreferably at greater than or equal to 80%, with respect to the totalamount of H⁺, H₂ ⁺, and H₃ ⁺ included in the ion beam 121.

In the case of performing ion irradiation by an ion-doping method withthe use of the hydrogen gas, the acceleration voltage can be set togreater or equal to 10 kV and less than or equal to 200 kV, and thedosage is set to greater than or equal to 1×10¹⁶ ions/cm² and less thanor equal to 6×10¹⁶ ions/cm². By the irradiation with the hydrogen ionsunder this condition, the embrittlement layer 103 can be formed at adepth of greater than or equal to 50 nm and less than or equal to 500 nmfrom the surface of the semiconductor substrate 101, though depending onthe ion species and its proportion in the ion beam 121.

Helium (He) can also be used as a source gas for the ion beam 121. Mostof ion species produced by excitation of helium is He⁺; therefore, He⁺can be mainly added to the semiconductor substrate 101 even by anion-doping method in which mass separation is not performed. Therefore,microvoids can be formed in the embrittlement layer 103 efficiently byan ion-doping method. When ion irradiation is performed using helium byan ion-doping method, the acceleration voltage can be set to greaterthan or equal to 10 kV and less than or equal to 200 kV, and the dosagecan be set to greater than or equal to 1×10¹⁶ ions/cm² and less than orequal to 6×10¹⁶ ions/cm².

A halogen gas such as a chlorine gas (Cl₂ gas) or a fluorine gas (F₂gas) can be used as the source gas.

Then, the insulating layer 105 is formed over the surface of thenitrogen-containing layer 104 (see FIG. 5C). As the insulating layer105, a smooth insulating layer having a hydrophilic surface ispreferable and a silicon oxide film is suitable. In particular, asilicon oxide film formed by a chemical vapor deposition method using anorganosilane gas is preferable. Examples of an organosilane gas that canbe used include silicon-containing compounds such as tetraethoxysilane(TEOS) (chemical formula: Si(OC₂H₅)₄), tetramethylsilane (TMS) (chemicalformula: Si(CH₃)₄), trimethylsilane (chemical formula: (CH₃)₃SiH),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (chemical formula:SiH(OC₂H₅)₃), and tris(dimethylamino)silane (chemical formula:SiH(N(CH₃)₂)₃). Note that a silicon oxynitride film may be used as theinsulating layer 105 instead of a silicon oxide film.

The insulating layer 105 is provided so as to have a thickness ofgreater than or equal to 5 nm and less than or equal to 500 nm. Withthis thickness, it is possible to smooth surface roughness of a surfaceof the insulating layer 105 (a surface on which bonding is performed)and also to ensure smoothness of a growing surface of the layer.Further, by provision of the insulating layer 102, thermal distortion ofthe glass substrate 110 and the semiconductor layer 122 can be relieved.In other words, the semiconductor layer 122 can be bonded to the glasssubstrate 110 strongly by providing the insulating layer 105 which isformed using a silicon oxide film deposited by using organosilane as asource gas over the surface of the semiconductor layer 122. The surfaceof the silicon oxide film is preferably set as follows: the averagesurface roughness (Ra) thereof is less than or equal to 0.5 nm and theroot-mean-square roughness (Rms) thereof is less than or equal to 0.6nm; more preferably, Ra is less than or equal to 0.3 nm and Rms is lessthan or equal to 0.4 nm.

Next, the semiconductor substrate 101 and the glass substrate 110 arebonded to each other with the insulating layer 105 and the altered layer111 interposed therebetween (see FIG. 5D). Here, the semiconductorsubstrate 101 and the glass substrate 110 are disposed in close contactwith each other and then a pressure of approximately 0.1 N/cm² to 50N/cm², preferably approximately 0.1 N/cm² to 20 N/cm² is applied to partof edge of the semiconductor substrate 101. The insulating layer 105 andthe altered layer 111 start bonding to each other from the part to whichthe pressure is applied and the bonded part spontaneously extendsthroughout the entire surface. This bonding step is performed by theaction of van der Waals forces. The bonding resulting from hydrogenbonding of Si—H or Si—OH can be performed by pressing the semiconductorsubstrate 101 and the glass substrate 110 against each other. Thisbonding step can be performed at a room temperature without heattreatment; therefore, a substrate whose upper limit temperature is lowlike the glass substrate 110 can be used.

Further, the altered layer 111 formed on at least the one surface of theglass substrate 110 has a lower density than the glass substrate 110;therefore, the altered layer 111 has small Yung's modulus and thus iseasily deformed. Accordingly, in the case where the insulating layer 105and the altered layer 111 are bonded to each other, even when a foreignmaterial exists on any of the surfaces thereof, the altered layer 111 isdeformed, so that unevenness due to the foreign material can be reduced.Therefore, a region in which bond is not formed in a periphery of theforeign material is reduced and the number of the regions is alsoreduced as compared to the case of bonding with the glass substrate 110not provided with the altered layer 111. Therefore, as compared to thecase where the insulating layer 105 and the glass substrate 110 arebonded to each other, a deficiency region of the semiconductor layer 122is reduced and thus the number of the deficiency regions is alsoreduced.

Note that before the bonding of the semiconductor substrate 101 and theglass substrate 110, surface treatment is preferably performed on theinsulating layer 105 formed over the semiconductor substrate 101 and thealtered layer 111 formed on the glass substrate 110. As the surfacetreatment, ozone treatment (for example, cleaning with ozone water),megasonic cleaning, two fluid cleaning (a cleaning method of sprayingwith functional water such as pure water or water to which hydrogen isadded together with a carrier gas such as nitrogen), or a combinationthereof can be employed. Cleaning with ozone water and cleaning withhydrofluoric acid may be performed on the insulating layer 105 formedover the semiconductor substrate 101 plural times. By performing suchsurface treatment, dust such as an organic material existing on thesurface of the insulating layer 105 and the surface of the altered layer111 is removed, whereby the surfaces of the insulating layer 105 and thealtered layer 111 become hydrophilic.

Here, an example of the ozone treatment different from cleaning withozone water is described. For example, by irradiation with ultravioletrays (UV) under an atmosphere including oxygen, ozone treatment can beperformed on a surface of a processing object. Ozone treatment in whichirradiation with ultraviolet rays is performed under an atmosphereincluding oxygen is also referred to as UV ozone treatment orultraviolet ozone treatment. By irradiation with light having awavelength of less than 200 nm of ultraviolet rays and light having awavelength of greater than 200 nm of ultraviolet rays under anatmosphere including oxygen, ozone is generated and singlet oxygen canbe generated from the ozone. By irradiation with light having awavelength of less than 180 nm of ultraviolet rays, ozone can begenerated and singlet oxygen can also be generated from the ozone.

The followings are examples of reactions resulted from the irradiationwith light having a wavelength of less than 200 nm and light having awavelength of greater than or equal to 200 nm under an atmosphereincluding oxygen.O₂ +hν(λ₁ nm)→O(³P)+O(³P)  (1)O(³P)+O₂→O₃  (2)O₃ +hν(λ₂ nm)→O(¹D)+O₂  (3)

In the above reaction formula (1), by irradiation with light (hν) havinga wavelength of less than 200 nm (λ₁ nm) under an atmosphere includingoxygen (O₂), oxygen atoms in a ground state (O(³P)) is generated. Next,in the above reaction formula (2), when an oxygen atom in a ground state(O(³P)) and oxygen (O₂) react to each other, ozone (O₃) is generated.Then, in the above reaction formula (3), by irradiation with lighthaving a wavelength of greater than or equal to 200 nm (λ₂ nm) under anatmosphere including ozone (O₃), singlet oxygen in an excited stateO(¹D) is generated. Ozone is generated by the irradiation with lighthaving a wavelength of less than 200 nm of ultraviolet rays under theatmosphere including oxygen and then decomposition of ozone is caused bythe irradiation with light having a wavelength of greater than or equalto 200 nm, whereby singlet oxygen is generated. The ozone treatmentdescribed above can be performed by irradiation with a low-pressuremercury lamp (λ₁=185 nm and λ₂=254 nm) under an atmosphere includingoxygen, for example.

Further, the following is an example of reactions resulted from theirradiation with light having a wavelength of less than 180 nm under anatmosphere including oxygen.O₂ +hν(λ₃ nm)→O(¹D)+O(³P)  (4)O(³P)+O₂→O₃  (5)O₃ +hν(λ₃ nm)→O(¹D)+O₂  (6)

In the above reaction formula (4), by irradiation with light having awavelength of less than 180 nm (λ₃ nm) under an atmosphere includingoxygen (O₂), singlet oxygen in an excited state (O(¹D)) and an oxygenatom in a ground state (O(³P)) are generated. Next, in the abovereaction formula (5), when an oxygen atom in a ground state (O(³P)) andoxygen (O₂) react to each other, ozone (O₃) is generated. In the abovereaction formula (6), by irradiation with light having a wavelength ofless than 180 nm (λ₃ nm) under an atmosphere including generated ozone(O₃), singlet oxygen in an excited state and oxygen are generated. Byperforming the irradiation with light having a wavelength of less than180 nm of ultraviolet rays under the atmosphere including oxygen, ozoneis generated and ozone or oxygen are decomposed to generate singletoxygen. The ozone treatment described above can be performed byirradiation with a Xe excimer UV lamp (λ₃=172 nm) under an atmosphereincluding oxygen, for example.

A chemical bond of an organic material or the like attached to a surfaceof a processing object can be broken by the light having a wavelength ofless than 200 nm and the organic material, the organic material whosechemical bond is broken, and the like attached to the surface of theprocessing object can be decomposed and removed by ozone or singletoxygen generated from ozone. By performing the ozone treatment describedabove, hydrophilicity and cleanliness of the surface of the processingobject can be increased and favorable bonding can be performed.

By irradiation with ultraviolet rays under an atmosphere includingoxygen, ozone is generated. Ozone has an effect of removing an organicmaterial attached to the surface of the processing object. Further,singlet oxygen also has an effect of removing an organic materialattached to the surface of the processing object, which is as effectiveas or more effective than ozone. Ozone and singlet oxygen are examplesof oxygen in an activated state and collectively referred to as activeoxygen. As described in the above reaction formulae and the like, thereis reaction of generation of ozone in generation of singlet oxygen orreaction of generation of singlet oxygen from ozone. Therefore, here,reactions including the reaction to which singlet oxygen contributes arereferred to as ozone treatment for convenience.

In addition, in order to perform a favorable bonding of thesemiconductor substrate 101 and the glass substrate 110, the surfaces ofthe altered layer 111 and the insulating layer 105 which are to bebonding surfaces may be activated in advance. For example, the surfacesof the altered layer 111 and the insulating layer 105 on which bondingis performed are irradiated with an atomic beam or an ion beam. When anatomic beam or an ion beam is used, an inert gas neutral atom beam orinert gas ion beam of argon or the like can be used. It is also possibleto activate the altered layer 111 and the insulating layer 105 by plasmairradiation or radical treatment. Such a surface treatment makes itpossible to easily perform bonding between different kinds of materialseven if heat treatment is performed at a temperature of less than 400°C.

Further, after the semiconductor substrate 101 and the glass substrate110 are bonded to each other with the insulating layer 105 and thealtered layer 111 interposed therebetween (see FIG. 6A), one or both ofheat treatment and pressure treatment are preferably performed. Byperforming heat treatment or pressure treatment, bonding strengthbetween the glass substrate 110 and the semiconductor substrate 101 canbe increased. The temperature of the heat treatment is lower than orequal to the upper limit temperature of the glass substrate 110. Forexample, the heat treatment is preferably performed at a temperature ofhigher than or equal to 200° C. and lower than or equal to 400° C. Thepressure treatment is performed so that pressure is applied in adirection perpendicular to the bonding surface, in consideration of thepressure resistance of the glass substrate 110 and the semiconductorsubstrate 101.

In general, when heat treatment is performed at such a temperature,bonding strength can be increased to some extent; however, it isdifficult to obtain enough bonding strength. This is because when heattreatment is performed after bonding of the semiconductor substrate andthe glass substrate, a dehydration condensation reaction occurs at thebonding interface and a covalent bond is generated, whereby the bondingstrength is increased; however, in order to promote the dehydrationcondensation reaction, moisture generated at the bonding interface dueto the dehydration condensation reaction needs to be removed by heattreatment at a high temperature. In other words, the moisture generatedat the bonding interface due to the dehydration condensation reactioncan be removed by increasing the heat treatment temperature after thebonding to increase the bonding strength. However, when the heattreatment temperature is low, the moisture generated at the bondinginterface due to the dehydration condensation reaction cannot be removedeffectively; therefore, the dehydration condensation reaction does notproceed and the bonding strength cannot be increased sufficiently.

However, in this embodiment, impurities, for example, movable ions ofalkali metal, alkaline earth metal and the like which contaminate thesemiconductor layer are reduced in the altered layer 111, wherebymicrovoids are formed in the film to increase moisture absorption rate.Accordingly, in the case where moisture exists on the surface of thealtered layer 111, the moisture is absorbed quickly and can be scatteredinto the altered layer 111. Therefore, regardless of the heat treatmenttemperature, the moisture generated at the bonding interface due to thedehydration condensation reaction is absorbed and scattered into thealtered layer 111, so that the dehydration condensation reaction can bepromoted efficiently. Thus, even if the heat treatment after the bondingis performed at a low temperature, strong covalent bond is formedbetween the insulating layer 105 over the semiconductor layer 122 andthe altered layer 111 on the glass substrate 110, so that the bondingstrength can be increased sufficiently. Accordingly, the deficiencyregion of the semiconductor layer 122 is reduced and thus the number ofthe deficiency regions is also reduced.

Next, heat treatment is performed, whereby part of the semiconductorsubstrate 101 is separated from the glass substrate 110, using theembrittlement layer 103 as a separation plane (see FIG. 6B). The heattreatment temperature is preferably higher than or equal to thedeposition temperature of the insulating layer 102 and is alsopreferably lower than or equal to the upper temperature limit of theglass substrate 110. When the heat treatment is performed at, forexample, a temperature of higher than or equal to 400° C. and less thanor equal to 700° C., microvoids formed in the embrittlement layer 103change in volume, whereby separation occurs along the embrittlementlayer 103. Since the insulating layer 105 is bonded to the altered layer111, the semiconductor layer 122, which has the same crystallinity asthe semiconductor substrate 101, remains over the glass substrate 110.Note that when the heat treatment is performed using an apparatus thatis capable of performing rapid heating, such as a rapid thermalannealing (RTA) apparatus, the heat treatment may be performed at atemperature higher than the strain point of the glass substrate 110.

In this manner, the insulating layer 105 over the semiconductor layer122 and the altered layer 111 on the glass substrate 110 are bonded toeach other and then heat treatment is performed plural times, wherebythe bonding strength can be increased. Note that heat treatment of FIG.6B may be performed without the aforementioned heat treatment forincreasing the bonding strength between the insulating layer 105 and thealtered layer 111, so that the heat treatment step for increasing thebonding strength of the insulating layer 105 and the altered layer 111and the heat treatment step for separation along the embrittlement layer103 may be performed at the same time.

Through the above steps, the SOI substrate, as illustrate in FIG. 1C, inwhich the semiconductor layer 122 is provided over the glass substrate110 with the insulating layer 102, the nitrogen-containing layer 104,and the insulating layer 105 interposed therebetween can be obtained.

Note that the method for manufacturing an SOI substrate, which isdescribed in this embodiment, is not limited to the above-describedmethod. For example, ions such as hydrogen may be added through theinsulating layer 102, the nitrogen-containing layer 104 and theinsulating layer 105 not before but after formation of the insulatinglayer 105, whereby the embrittlement layer 103 may be formed in a regionat a predetermined depth from the surface of the semiconductor substrate101. A surface layer of the insulating layer 105 may be etched afterions are added, whereby a damaged layer formed over the surface of theinsulating layer 105 due to the addition of ions may be removed.Further, after silane is adsorbed onto the surface of the insulatinglayer 105, the insulating layer 105 may exposed to the air to form athin oxide film (for example, SiOx) over the insulating layer 105,whereby the insulating layer 105 may be flattened. Note that the bondingsurface may be activated by performing plasma irradiation or radicaltreatment on the surface after the oxide film is formed.

Alternatively, ions such as hydrogen may be added not after but beforethe formation of the insulating layer 102 and the nitrogen-containinglayer 104, whereby the embrittlement layer 103 is formed in a region ata predetermined depth from the surface of the semiconductor substrate101. Note that in this case, it is preferable that a protective layer beformed over the surface of the semiconductor substrate 101 and then ionsbe added through the protective layer in order to prevent impurities andthe like from attaching to the surface of the semiconductor substrate101 due to addition of ions and to prevent the surface of thesemiconductor substrate 101 from being etched due to addition of ions.

As the protective layer, for example, an oxide film which is obtained byperforming treatment on the surface of the semiconductor substrate 101with ozone water, a hydrogen peroxide solution, and a sulfuricacid/hydrogen peroxide mixture in an ozone atmosphere can be used.Alternatively, an oxide film which is obtained by performing oxidationin which halogen is added in an oxidation atmosphere can be used as theprotective layer. In the case where a halogen element is included in anoxide film, the oxide film can function as a protective layer whichcaptures impurities such as metals and prevents the semiconductorsubstrate 101 from being contaminated.

After that, the insulating layer 102, the nitrogen-containing layer 104and the insulating layer 105 may be formed over the protective layerformed over the semiconductor substrate 101, or the insulating layer102, the nitrogen-containing layer 104 and the insulating layer 105 maybe formed over the semiconductor substrate 101 after the protectivelayer is removed after ion introduction.

Further, the SOI substrate in which the insulating layer 105 is notformed over the surface of the nitrogen-containing layer 104 may beemployed. In this case, the SOI substrate illustrated in FIG. 1B inwhich the semiconductor layer 122 is provided over the glass substrate110 with the insulating layer 102 and the nitrogen-containing layer 104interposed therebetween can be obtained. When the insulating layer 105is not formed, an insulating layer having a smooth surface is preferablyused for the nitrogen-containing layer 104 since the nitrogen-containinglayer 104 functions as the bonding layer for bonding with the alteredlayer 111. It is preferable that the nitrogen-containing layer 104 beformed so that the mean surface roughness (Ra) is less than or equal to0.5 nm and the root-mean-square roughness (Rms) is less than or equal to0.6 nm; more preferably, Ra is less than or equal to 0.3 nm and Rms isless than or equal to 0.4 nm. A silicon oxynitride film or a siliconnitride oxide film which is deposited by a plasma CVD method at a lowtemperature (higher than or equal to 100° C. and lower than or equal to350° C.; preferably higher than or equal to 150° C. and lower than orequal to 300° C.) is suitable as the nitrogen-containing layer 104. Byperforming deposition by a plasma CVD method at a low temperature, asilicon oxynitride film or a silicon nitride oxide film which has asmooth surface can be obtained. Further, by performing deposition of thenitrogen-containing layer 104 at a low temperature, the amount ofhydrogen (H) included in the film can be increased, which enable strongbonding of the glass substrate 110 and the altered layer 111.

Further, by providing a silicon oxide film having a smooth surface asthe insulating layer 102, a surface of the nitrogen-containing layer 104formed over the insulating layer 102 can be flattened. Note that whenthe semiconductor substrate 101 has a flat surface, a structure withoutthe insulating layer 102 may be employed. For example, thenitrogen-containing layer 104 can be formed of a single layer selectedfrom a silicon oxynitride film or a silicon nitride oxide film or can beformed of a laminate of layers of a silicon oxynitride film and asilicon nitride oxide film which are stacked on the semiconductorsubstrate 101 side.

Further, after ion introduction is performed through thenitrogen-containing layer 104 and silane is adsorbed onto the surface ofthe nitrogen-containing layer 104, the surface of thenitrogen-containing layer 104 is exposed to the air, whereby a thinoxide film (for example, SiOx) may be formed over thenitrogen-containing layer 104. In this case, the surface of thenitrogen-containing layer 104 can be hydrophilic after the ionintroduction, and the bonding with the glass substrate 110 can bestrengthened. Note that the bonding surface may be activated byperforming plasma irradiation or radical treatment on the surface afterthe oxide film is formed.

Alternatively, the SOI substrate in which the nitrogen-containing layer104 is not formed over the surface of the insulating layer 102 may beemployed. In this case, the SOI substrate illustrated in FIG. 1A inwhich the semiconductor layer 122 is provided over the glass substrate110 with the insulating layer 102 interposed therebetween can beobtained. When the nitrogen-containing layer 104 is not formed, aninsulating layer having a smooth surface is preferably used for theinsulating layer 102 because the surface of the insulating layer 102 isto be the bonding surface for bonding with the altered layer 111;therefore a silicon oxide film is suitable for the insulating layer 102.In particular, a silicon oxide film deposited by a chemical vapordeposition method using an organosilane gas is preferable. This isbecause the insulating layer 102 can have a flat surface when formedwith a silicon oxide film using an organosilane gas. It is preferablethat the silicon oxide film be formed so that the mean surface roughness(Ra) thereof is less than or equal to 0.5 nm and the root-mean-squareroughness (Rms) thereof is less than or equal to 0.6 nm; morepreferably, Ra thereof is less than or equal to 0.3 nm and Rms thereofis less than or equal to 0.4 nm.

Examples of the organosilane gas include silicon-containing compoundssuch as tetraethoxysilane (TEOS) (chemical formula: Si(OC₂H₅)₄),tetramethylsilane (TMS) (chemical formula: Si(CH₃)₄), trimethylsilane(chemical formula: (CH₃)₃SiH), tetramethylcyclotetrasiloxane (TMCTS),octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS),triethoxysilane (chemical formula: SiH(OC₂H₅)₃), andtris(dimethylamino)silane (chemical formula: SiH(N(CH₃)₂)₃).

Note that in the above process, flattening treatment may be performed ona surface of the obtained SOI substrate. By performing the flatteningtreatment, even when the semiconductor layer 122 provided over the glasssubstrate 110 has an uneven surface after separation, the surface of theSOI substrate can be flattened.

For the flattening treatment, CMP (chemical mechanical polishing),etching treatment, laser light irradiation, or the like can beperformed. Etching treatment (etch-back treatment) which is dry etching,wet etching, or a combination of dry etching and wet etching isperformed and then irradiation with a laser beam is performed, wherebythe semiconductor layer 122 is recrystallized and the surface thereof isflattened.

By irradiation with the laser beam through the top surface of thesemiconductor layer 122, the top surface of the semiconductor layer 122can be melted. After being melted, the semiconductor layer 122 is cooledand solidified, so that a single crystal semiconductor film having thetop surface whose flatness is improved can be obtained. By using a laserbeam for irradiation, since the glass substrate 110 is not directlyheated, increase in temperature of the glass substrate 110 can besuppressed. Therefore, a low-heat-resistant substrate such as a glasssubstrate can be used as the glass substrate 110.

Note that it is preferable that the semiconductor layer 122 be partiallymelted by the laser beam irradiation. This is because, if thesemiconductor layer is completely melted, it is microcrystallized due todisordered nucleation after being in a liquid phase, so thatcrystallinity of the semiconductor layer is highly likely to decrease.On the contrary, by partial melting, crystal growth proceeds from asolid phase part which is not melted. Accordingly, defects in thesemiconductor film can be reduced. Here, “complete melting” refers tothat the semiconductor layer is melted down to the vicinity of the lowerinterface thereof to be made in a liquid state. On the other hand, inthis case, “partial melting” refers to that the upper part of thesemiconductor layer is melted to be made in a liquid phase while thelower part thereof is not melted and is still in a solid phase.

A pulsed laser is preferably used for the laser irradiation. This isbecause a pulsed laser light with high energy can be emittedinstantaneously and a liquid phase can be easily obtained. Therepetition rate is preferably approximately 1 Hz to 10 MHz, inclusive.

After the irradiation with the laser beam as described above, a step ofthinning the semiconductor layer 122 may be performed. In order to thinthe semiconductor layer 122, etching treatment (etch-back treatment)which is dry etching, wet etching or a combination of dry etching andwet etching may be applied. For example, when the semiconductor layer122 is formed using a silicon material, the semiconductor layer 122 canbe thinned by dry etching using SF₆ and O₂ or only Cl₂ as a process gas.

In this manner, even when the glass substrate is used as a basesubstrate of the SOI substrate, the deficiency region of thesemiconductor layer can be reduced; therefore, the SOI substrateprovided with the semiconductor layer which can be used practically canbe manufactured.

Note that the method for manufacturing an SOI substrate described inthis embodiment can be combined with manufacturing methods in otherembodiment in this specification, as appropriate.

Embodiment 3

In this embodiment, a method for manufacturing a semiconductor deviceusing the SOI substrate described in Embodiment 1 is described.

First, a method for manufacturing an n-channel thin film transistor anda p-channel thin film transistor is described as a method formanufacturing a semiconductor device with reference to FIGS. 7A to 7Dand 8A to 8C. Various kinds of semiconductor devices can be formed bycombining a plurality of thin film transistors (TFTs).

The SOI substrate of FIG. 1C which is manufactured according to themethod of Embodiment 2 is used as an SOI substrate. FIG. 7A is a crosssectional view illustrating the SOI substrate of FIG. 1C manufactured bya method described with reference to FIGS. 3A and 3B, FIGS. 4A and 4B,FIGS. 5A to 5D and FIGS. 6A and 6B.

The semiconductor layer 122 of the SOI substrate is isolated into eachelement by etching, thereby forming semiconductor layers 151 and 152 asillustrated in FIG. 7B. The semiconductor layer 151 constitutes part ofan n-channel TFT, and the semiconductor layer 152 constitutes part of ap-channel TFT.

As illustrated in FIG. 7C, an insulating layer 154 is formed over thesemiconductor layers 151 and 152. And then, a gate electrode 155 isformed over the semiconductor layer 151 with the insulating layer 154interposed therebetween, and a gate electrode 156 is formed over thesemiconductor layer 152 with the insulating layer 154 interposedtherebetween.

Note that before the semiconductor layer 122 is etched, it is preferableto add an impurity element which functions as an acceptor, such asboron, aluminum, or gallium, or an impurity element which functions as adonor, such as phosphorus or arsenic, to the semiconductor layer 122 inorder to control the threshold voltage of the TFTs. For example, anacceptor is added to a region where an n-channel TFT is formed and adonor is added to a region where a p-channel TFT is formed.

Next, as illustrated in FIG. 7D, n-type low-concentration impurityregions 157 and p-type high-concentration impurity regions 159 areformed in the semiconductor layers 151 and 152 respectively. First, then-type low-concentration impurity regions 157 are formed in thesemiconductor layer 151. In order to form the n-type low-concentrationimpurity regions 157, the semiconductor layer 152 used for a p-channelTFT is covered with a resist mask, and a donor is added to thesemiconductor layer 151. As the donor, arsenic may be added. When thedonor is added by an ion-doping method or an ion-implantation method,the gate electrode 155 functions as a mask and thus the n-typelow-concentration impurity regions 157 are formed in the semiconductorlayer 151 in a self-aligning manner. A region of the semiconductor layer151 that overlaps with the gate electrode 155 functions as a channelformation region 158.

Next, after removing the mask which covers the semiconductor layer 152,the semiconductor layer 151 used for an n-channel TFT is formed iscovered with a resist mask. Next, an acceptor is added to thesemiconductor layer 152 by an ion-doping method or an ion-implantationmethod. Boron can be added as the acceptor. In the step of adding theacceptor, since the gate electrode 156 functions as a mask, the p-typehigh-concentration impurity regions 159 are formed in the semiconductorlayer 152 in a self-aligning manner. The high-concentration impurityregions 159 function as a source region and a drain region. A region ofthe semiconductor layer 152 which overlaps with the gate electrode 156functions as a channel formation region 160. Here, explanation has beenmade on the method in which the p-type high-concentration impurityregions 159 are formed after forming the n-type low-concentrationimpurity regions 157; however, the p-type high-concentration impurityregions 159 can be formed first.

Next, after removing the resist that covers the semiconductor layer 151,an insulating film having a single-layer structure or a stacked layerstructure which includes a nitrogen compound such as silicon nitride oran oxide such as silicon oxide is formed by a plasma CVD method or thelike. This insulating layer is anisotropically-etched in a perpendiculardirection, so that side-wall insulating layers 161 and 162 which are incontact with the side surfaces of the gate electrodes 155 and 156respectively are formed as illustrated in FIG. 8A. By this anisotropicetching, the insulating layer 154 is also etched.

Next, the semiconductor layer 152 is covered with a resist 165, asillustrated in FIG. 8B. In order to form the high-concentration impurityregions functioning as a source region and a drain region in thesemiconductor layer 151, a large dosage of donors are added to thesemiconductor layer 151 by an ion-doping method or an ion-implantationmethod. The gate electrode 155 and the side-wall insulating layer 161function as a mask, and n-type high-concentration impurity regions 167are formed. Next, heat treatment for activating the donors and theacceptors is performed.

After the heat treatment for activation, as illustrated in FIG. 8C, aninsulating layer 168 including hydrogen is formed. After forming theinsulating layer 168, heat treatment is performed at temperatures ofhigher than or equal to 350° C. and lower than or equal to 450° C., sothat hydrogen in the insulating layer 168 is diffused into thesemiconductor layers 151 and 152. The insulating layer 168 can be formedby depositing silicon nitride or silicon nitride oxide by a plasma CVDmethod at less than or equal to 350° C. By supplying hydrogen into thesemiconductor layers 151 and 152, defects which turn into trappingcenters in the semiconductor layers 151 and 152 or at an interfacebetween the semiconductor layers 151 and 152 and the insulating layer154 can be effectively compensated.

After that, an interlayer insulating layer 169 is formed. The interlayerinsulating layer 169 can be formed using a film with a single layerstructure or a stacked layer structure which is formed of any one ormore of films selected from an insulating film containing an inorganicmaterial such as a silicon oxide film or a BPSG (boron phosphorussilicon glass) film, or an organic resin film containing polyimide,acrylic, or the like. Contact holes are formed in the interlayerinsulating layer 169, wirings 170 are formed as illustrated in FIG. 8C.The wirings 170 can be formed using a conductive film with a three-layerstructure in which a low-resistance metal film such as an aluminum filmor an aluminum-alloy film is sandwiched between barrier metal films. Thebarrier metal films can be formed using metal films which includemolybdenum, chromium, titanium, and/or the like.

Through the above steps, a semiconductor device having the n-channel TFTand the p-channel TFT can be manufactured. Since the deficiency regionof the semiconductor layer is reduced in a process for manufacturing theSOI substrate as described in Embodiment 1 and Embodiment 2, TFTs havinghigh reliability can be manufactured.

Although the method for manufacturing TFTs is described with referenceto FIGS. 7A to 7D and 8A to 8C, a semiconductor device with high addedvalue can be manufactured by forming a variety of semiconductor elementssuch as a capacitor and a resistor together with the TFTs. Hereinafter,specific embodiments of the semiconductor device will be described withreference with drawings.

First, a microprocessor is described as an example of a semiconductordevice. FIG. 9 is a block diagram illustrating a structural example of amicroprocessor 500.

The microprocessor 500 includes an arithmetic logic unit (also referredto as an ALU) 501, an ALU controller 502, an instruction decoder 503, aninterrupt controller 504, a timing controller 505, a register 506, aregister controller 507, a bus interface (Bus I/F) 508, a read-onlymemory (ROM) 509, and a ROM interface 510.

An instruction input to the microprocessor 500 via the bus interface 508is input to the instruction decoder 503 and decoded. Then, theinstruction is input to the ALU controller 502, the interrupt controller504, the register controller 507, and the timing controller 505. The ALUcontroller 502, the interrupt controller 504, the register controller507, and the timing controller 505 perform various controls based on thedecoded instruction.

The ALU controller 502 generates signals for controlling the operationof the ALU 501. While the microprocessor 500 is executing a program, theinterrupt controller 504 judges an interrupt request from an externalinput and output device or a peripheral circuit based on its priority ora mask state, and processes the interrupt request. The registercontroller 507 generates an address of the register 506, andreads/writes data from/to the register 506 in accordance with the stateof the microprocessor 500. The timing controller 505 generates signalsfor controlling timing of driving of the arithmetic logic unit 501, theALU controller 502, the instruction decoder 503, the interruptcontroller 504, and the register controller 507. For example, the timingcontroller 505 is provided with an internal clock generator forgenerating an internal clock signal CLK2 based on a reference clocksignal CLK1. As shown in FIG. 9, the internal clock signal CLK2 is inputto another circuit.

Next, an example of a semiconductor device having a function ofcommunicating data wirelessly and also having an arithmetic function isdescribed. FIG. 10 is a block diagram showing a structural example ofsuch a semiconductor device. The semiconductor device shown in FIG. 10can be regarded as a computer (hereinafter also referred to as an“RFCPU”) which operates to transmit/receive signals to/from an externaldevice by radio communication.

As shown in FIG. 10, an RFCPU 511 includes an analog circuit portion 512and a digital circuit portion 513. The analog circuit portion 512includes a resonance circuit 514 having a resonant capacitor, arectifier circuit 515, a constant voltage circuit 516, a reset circuit517, an oscillator circuit 518, a demodulation circuit 519, a modulationcircuit 520, and a power supply control circuit 530. The digital circuitportion 513 includes an RF interface 521, a control register 522, aclock controller 523, a CPU interface 524, a central processing unit(CPU) 525, a random access memory (RAM) 526, and a read only memory(ROM) 527.

The operation of the RFCPU 511 is roughly described below. The resonancecircuit 514 generates induced electromotive force based on a signalreceived at an antenna 528. The induced electromotive force is stored ina capacitor portion 529 via the rectifier circuit 515. The capacitorportion 529 is preferably formed using a capacitor such as a ceramiccapacitor or an electric double layer capacitor. The capacitor portion529 is not necessarily integrated over the same substrate as the RFCPU511 and may be incorporated into the RFCPU 511 as a component.

The reset circuit 517 generates signals for resetting the digitalcircuit portion 513 and initializing the digital circuit portion 513.For example, the reset circuit generates a signal which rises after risein the supply voltage with delay as a reset signal. The oscillatorcircuit 518 changes the frequency and the duty ratio of a clock signalin accordance with a control signal generated by the constant voltagecircuit 516. The demodulation circuit 519 demodulates a received signal,and the modulation circuit 520 modulates data to be transmitted.

For example, the demodulation circuit 519 is formed using a low-passfilter and binarizes a received signal of an amplitude shift keying(ASK) system based on variation of the amplitude. The modulation circuit520 transmits transmission data by changing the amplitude of atransmission signal of the amplitude shift keying (ASK) system. Themodulation circuit 520 changes the resonance point of the resonancecircuit 514, whereby the amplitude of a communication signal is changed.

The clock controller 523 generates a control signal for changing thefrequency and the duty ratio of the clock signal in accordance with thepower supply voltage or current consumption in the central processingunit 525. The power supply voltage is monitored by the power supplycontrol circuit 530.

A signal that is input to the RFCPU 511 from the antenna 528 isdemodulated by the demodulation circuit 519, and then divided into acontrol command, data, and the like by the RF interface 521. The controlcommand is stored in the control register 522. The control commandincludes reading of data stored in the read only memory 527, writing ofdata to the random access memory 526, an arithmetic instruction to thecentral processing unit 525, and the like.

The central processing unit 525 accesses the read only memory 527, therandom access memory 526, and the control register 522 via the CPUinterface 524. The CPU interface 524 has a function of generating anaccess signal for any one of the read only memory 527, the random accessmemory 526, and the control register 522 based on an address requestedby the central processing unit 525.

As an arithmetic method of the central processing unit 525, a method maybe employed in which the read only memory 527 stores an OS (operatingsystem) and a program is read at the time of starting operation and thenexecuted. Alternatively, a method in which a circuit dedicated toarithmetic is formed and an arithmetic process is conducted usinghardware may be employed. In a method in which both hardware andsoftware are used, part of arithmetic processing can be conducted by acircuit dedicated to arithmetic, and the other part of the arithmeticprocessing can be conducted by the central processing unit 525 using aprogram.

Next, a display device as a semiconductor device is described withreference to FIG. 11, FIGS. 12A and 12B, and FIGS. 13A and 13B.

In the SOI substrate described in Embodiment 1, the glass substrate 110can be applied for the base substrate. Therefore, by using the glasssubstrate 110 as the base substrate and bonding a plurality ofsemiconductor layers thereto, a large-sized SOI substrate with each sideover one meter in length can be manufactured.

A large-area glass substrate called mother glass for manufacturing adisplay panel can be used as a glass substrate of an SOI substrate. FIG.11 is a front view of an SOI substrate in which mother glass is used asthe glass substrate. With a plurality of semiconductor elements formedusing such a large-area SOI substrate, a liquid crystal display deviceor an electroluminescent display device can be manufactured. In additionto such display devices, various kinds of semiconductor devices such asa solar cell, a photo IC, and a semiconductor memory device can bemanufactured using the SOI substrate.

As illustrated in FIG. 11, single crystal semiconductor layers 302 whichare separated from a plurality of semiconductor substrates are bonded toone mother glass 301. In order to cut out a plurality of display panelsfrom the mother glass 301, formation regions 310 of the display panelsare preferably included in the single crystal semiconductor layers 302.Each of the display panels includes a scanning line driver circuit, asignal line driver circuit, and a pixel portion. Therefore, theformation regions 310 of the display panels include a region where ascanning line driver circuit formation region 311, a signal line drivercircuit formation region 312, and a pixel formation region 313 areformed.

FIGS. 12A and 12B are drawings for describing a liquid crystal displaydevice. FIG. 12A is a plane view of a pixel of the liquid crystaldisplay device, and FIG. 12B is a cross-sectional view taken along aline J-K in FIG. 12A.

As illustrated in FIG. 12A, the pixel includes a single crystalsemiconductor layer 320, a scanning line 322 intersecting with thesingle crystal semiconductor layer 320, a signal line 323 intersectingwith the scanning line 322, a pixel electrode 324, and an electrode 328which electrically connects the pixel electrode 324 with the singlecrystal semiconductor layer 320. The single crystal semiconductor layer320 is a layer illustrated in FIG. 11 formed using the single crystalsemiconductor layer 302 bonded to the SOI substrate and is included in aTFT 325 of the pixel.

As the SOI substrate, the SOI substrate described in Embodiment 1 isused. As illustrated in FIG. 12B, the insulating layer 105, thenitrogen-containing layer 104, the insulating layer 102, and the singlecrystal semiconductor layer 320 are stacked over the glass substrate 110having one surface on which the altered layer 111 is formed. The glasssubstrate 110 is the mother glass 301 which has been divided. The singlecrystal semiconductor layer 320 of the TFT 325 is formed by elementisolation of the semiconductor layer of the SOI substrate by etching. Achannel formation region 340 and n-type high-concentration impurityregions 341 to which donors are added are formed in the single crystalsemiconductor layer 320. A gate electrode of the TFT 325 is included inthe scanning line 322 and one of a source electrode and a drainelectrode of the TFT 325 is included in the signal line 323.

The signal line 323, the pixel electrode 324, and the electrode 328 areprovided over the interlayer insulating film 327. Columnar spacers 329are formed over the interlayer insulating film 327. An orientation film330 is formed so as to cover the signal line 323, the pixel electrode324, the electrode 328, and the columnar spacers 329. A countersubstrate 332 is provided with a counter electrode 333 and anorientation film 334 which covers the counter electrode 333. Thecolumnar spacers 329 are formed in order to maintain a space between theglass substrate 110 and the counter substrate 332. A liquid crystallayer 335 is formed in the space formed by the column spacers 329. Theinterlayer insulating film 327 has a step at the connection portionbetween the high-concentration impurity regions 341, and the signal line323 and the electrode 328 due to formation of contact holes; therefore,orientation of liquid crystals in the liquid crystal layer 335 is likelyto be disordered at this connection portion. Therefore, the columnarspacers 329 are formed at these step portions to prevent disorder ofliquid crystal orientation.

Next, an electroluminescent display device (hereinafter referred to asan EL display device) is described with reference to FIGS. 13A and 13B.FIG. 13A is a plan view of a pixel of an EL display device and FIG. 13Bis a cross-sectional view taken along a line J-K of FIG. 13A.

As illustrated in FIG. 13A, the pixel includes a selection transistor401 and a display control transistor 402 each including a TFT, ascanning line 405, a signal line 406, a current supply line 407, and apixel electrode 408. In the EL display device, each pixel is providedwith a light-emitting element having a structure in which a layerincluding an electroluminescent material (this layer is also referred toas an EL layer) is sandwiched between a pair of electrodes. Oneelectrode of the light emitting element is the pixel electrode 408.Further, in a semiconductor layer 403, a channel formation region, asource region, and a drain region of the selection transistor 401 areformed. Further, in a semiconductor layer 404, a channel formationregion, a source region, and a drain region of the display controltransistor 402 are formed. The semiconductor layers 403 and 404 arelayers illustrated in FIG. 11 formed using the single crystalsemiconductor layer 302 bonded to the SOI substrate.

In the selection transistor 401, a gate electrode is included in thescanning line 405, one of a source electrode and a drain electrode isincluded in the signal line 406 and the other thereof is formed as anelectrode 411. In the display control transistor 402, a gate electrode412 is electrically connected to the electrode 411, one of a sourceelectrode and a drain electrode is formed as an electrode 413 which iselectrically connected to the pixel electrode 408, and the other thereofis included in the current supply line 407.

The display control transistor 402 is a p-channel TFT. As illustrated inFIG. 13B, a channel formation region 451 and p-type high-concentrationimpurity regions 452 are formed in the semiconductor layer 404. As anSOI substrate, the SOI substrate manufactured according to the method ofEmbodiment 2 is used.

An interlayer insulating film 427 is formed so as to cover the gateelectrode 412 of the display control transistor 402. The signal line406, the current supply line 407, the electrode 411, the electrode 413,and the like are formed over the interlayer insulating film 427.Further, the pixel electrode 408 which is electrically connected to theelectrode 413 is formed over the interlayer insulating film 427. Aperipheral portion of the pixel electrode 408 is surrounded by apartition wall layer 428 having an insulating property. The EL layer 429is formed over the pixel electrode 408, and a counter electrode 430 isformed over the EL layer 429. A counter substrate 431 is provided as areinforcing plate and is fixed to the glass substrate 110 by a resinlayer 432.

The grayscale of the EL display device is controlled by either a currentdrive method by which the luminance of the light-emitting element iscontrolled by the amount of current or a voltage drive method by whichcontrol is performed basically by the amount of voltage. The currentdrive method is difficult to adapt when transistors have characteristicswhich are largely different for each pixel, and therefore a compensationcircuit for compensating variation in characteristics is necessary. TheEL display device is manufactured by a manufacturing process of an SOIsubstrate and a manufacturing method including a gettering step so thatthe selection transistor 401 and the display control transistor 402 donot have variation in characteristics in each pixel. Accordingly, thecurrent driving method can be employed.

Namely, various electronic appliances can be manufactured by using SOIsubstrates. The electronic appliances include, in its category, camerassuch as video cameras, digital cameras, navigation systems, audioreproducing devices (such as car audios or audio components), computers,game machines, portable information terminals (such as mobile computers,mobile phones, portable game machines, or e-book readers), and imagereproducing devices having storage media (specifically, devices providedwith display devices capable of playing audio data stored in recordingmedia such as digital versatile disk (DVD) and displaying stored imagedata).

Specific modes of the electronic appliances is described using FIGS. 14Ato 14C. FIG. 14A is an external view illustrating an example of acellular phone 901. This cellular phone 901 includes a display portion902, operation switches 903 and the like. The liquid crystal displaydevice illustrated in FIGS. 12A and 12B or the EL display deviceillustrated in FIGS. 13A and 13B is applied to the display portion 902,whereby the display portion 902 can have little display unevenness andexcellent image quality.

FIG. 14B is an external view illustrating a structural example of adigital player 911. The digital player 911 includes a display portion912, an operation portion 913, an earphone 914, and the like. Instead ofthe earphone 914, a headphone or a wireless earphone can be used. Byapplying the liquid crystal display device described illustrated inFIGS. 12A and 12B or the EL display device illustrated in FIGS. 13A and13B to the display portion 912, even in the case where the screen sizeis about 0.3 inches to 2 inches, an image with high precision and alarge amount of text information can be displayed.

Further, FIG. 14C is an external view of an electronic book 921. Thiselectronic book 921 includes a display portion 922 and operationswitches 923. A modem may be incorporated in the electronic book reader921, or the RFCPU in FIG. 10 may be incorporated therein so that theelectronic book reader 921 has a structure with which information can betransmitted and received wirelessly. By applying the liquid crystaldisplay device illustrated in FIGS. 12A and 12B or the EL display deviceillustrated in FIGS. 13A and 13B to the display portion 922, an imagewith high image quality can be displayed.

Example 1

This example describes evaluation results of an altered layer which isformed on at least one surface of a glass substrate according to thepresent invention.

In this example, a glass substrate A in which an altered layer is formedon its surface layer by HPM treatment and an untreated glass substrate Bare prepared. Each surface thereof is measured by X-ray reflectivity(XRR) measurement and X-ray photoelectron spectroscopy (XPS).

Here, the XRR measurement refers to a measurement method in which:X-rays enter a flat thin film at a very shallow incident angle; and thethickness, density and flatness of the thin film are measured byutilizing a phenomenon in which X-rays reflected at an surface of thethin film and an interface between the thin film and the substrateinterfere with each other. Note that a measurement region of the XRRmeasurement is a quadrangle region having a size of 8 nm to 15 nmsquare. Since measurement is performed changing the incident angle ofX-rays, the measurement region is changed in accordance with theincident angle of the X-rays. Further, the thickness, density andflatness are calculated from the average value of the intensity ofX-rays which are reflected at respective parts of the measurementregion.

In addition, the XPS refers to a method in which the energy distributionof photoelectron emitted by irradiating a sample with X-rays is detectedand findings about the kind, the number and chemical condition ofelements on a surface of the sample are obtained.

The samples used in this example are described. As the glass substratesA and B, non-alkali glass substrates (the trade name is AN 100)manufactured by ASAHI GLASS CO., LTD. were used. Note that thenon-alkali glass includes an extremely small number of alkali metal andalkaline earth metal although called “a non-alkali glass”. Eachthickness of the glass substrates A and B was 0.7 mm. Of them, the glasssubstrate A was provided with an altered layer on its surface layer byHPM treatment.

The samples were manufactured as follows. First, hydrochloric acid, ahydrogen peroxide solution and pure water were mixed with a ratio of1:1:5 to generate a hydrochloric acid/hydrogen peroxide solution mixture(HPM). Next, the glass substrate A was soaked in a cleaning bath filledwith HPM solution having a temperature of 70° C., for 10 minutes. Afterthat, the glass substrate A was soaked in a cleaning bath filled withpure water for 10 minutes and then dried with a rinser dryer to removewater droplets on the glass substrate. In this manner, the altered layerwas formed on the surface of the glass substrate A. The glass substrateB was left untreated.

TABLE 1 density thickness sample layer (g/cm3) (nm) roughness (nm) glasssubstrate A altered layer 2.06 9.22 0.8 intermediate 2.23 2.4 0.83 layerglass layer 2.5 0.92 glass substrate B glass layer 2.5 0.92

Data shown in Table 1 is obtained in such a manner that fitting isperformed on the measurement results of the X-ray reflection intensityof the glass substrate A and the glass substrate B by the XRRmeasurement, by performing simulation employing a model in which thealtered layer has two layers which differ in density. Note that in theXRR measurement of this example, the measurement region at the start ofthe measurement is a quadrangle region having a size of 10 mm in adirection of travel of X-rays and 8 mm in a direction perpendicularthereto at the center of the glass substrate; the measurement region atthe termination of the measurement is a quadrangle region having a sizeof 8 mm in the direction of travel of X-rays and 8 mm in the directionperpendicular thereto. According to Table 1, it is shown that thedensity of a glass layer of the glass substrate A is the same as that ofthe untreated glass substrate B and the density of the altered layer(its thickness is 9.22 nm) of the glass substrate A subjected to HPMtreatment is lower than that of the glass layer thereof. In addition,the roughness of the altered layer of the glass substrate A is smallerthan that of each glass layer of the glass substrate A and the glasssubstrate B. Further, it can be found that an intermediate layer (itsthickness is 2.4 nm) having density and roughness which are betweenthose of the glass layer and those of the altered layer is formedbetween the glass layer and the altered layer of the glass substrate A.

In addition, STEM (scanning transmission electron microscope) images ofthe surface portions of the glass substrate A and the glass substrate Bare shown in FIGS. 15A and 15B, respectively. By comparison betweenFIGS. 15A and 15B, an altered layer 1001 with a thickness ofapproximately 9.3 nm certainly exists on a glass layer 1000 in FIG. 15A,which attests the results of XRR measurement. Note that films over theglass substrates in FIGS. 15A and 15B are films of carbon and metal fortaking STEM images.

TABLE 2 sample Si O Al Sr B Ca Mg (atomic %) (atomic %) (atomic %)(atomic %) (atomic %) (atomic %) (atomic %) glass substrate A 28.4 70.70.8 0.1 — — — glass substrate B 21.5 66.8 5.9 1.2 3 1.1 0.4

Measurement results of the glass substrate A and the glass substrate Bby the XPS are shown in Table 2. In the XPS of this example, QuanteraSXM manufactured by PHI incorporated was used as a measurement apparatusand monochromatic AlKα ray (1.486 keV) was used for an X-ray source. Thediameter of a detection region was set to 100 μm and the depth thereofwas set to greater than or equal to 4 nm and less than or equal to 5 nm.According to Table 2, it is shown that alkaline earth metal atoms of Sr,Ca and Mg, metal atoms of Al and B, and the like, which exist over thesurface of the untreated glass substrate B at a concentration of severalat. %, exist over the glass substrate A after the HPM treatment at aconcentration of less than 1 at. % or less than the lower limit of thedetection. In a similar manner, it is presumed that impurities such asalkali metal atoms which exist at a concentration less than the lowerlimit of the detection are reduced. Further, existence ratio of Si andthat of O at the surface of the glass substrate A are relativelyincreased as compared with those at the surface of the glass substrateB.

Next, the photoelectron spectroscopy spectra of Si-2p orbitals of theglass substrate A and the glass substrate B, and the photoelectronspectroscopy spectra of O-1s orbitals of the glass substrate A and theglass substrate B are shown in FIG. 16 and FIG. 17, respectively.According to FIG. 16 and FIG. 17, in each of the photoelectronspectroscopy spectra of the Si-2p orbitals of the glass substrate A andthe glass substrate B and the O-1s orbitals thereof, a peakcorresponding to chemical shift of SiO₂ appears. In each ofphotoelectron spectroscopy spectra of the Si-2p orbitals and the O-1sorbitals, a peak corresponding to the chemical shift of SiO₂ of theglass substrate A is sharper than that of the glass substrate B.Accordingly, it is understood that Si and O which are relativelyincreased in existence ratio at the surface layer of the glass substrateA mainly form silicon oxide (SiO₂).

Accordingly, it was found that when the HPM treatment was performed onthe glass substrate, the altered layer having a higher proposition ofsilicon oxide in its composition and a lower density than the glasslayer was formed on the surface layer of the glass substrate.

Example 2

In this example, evaluation results of a deficiency region of a singlecrystal silicon film of an SOI substrate manufactured according to thepresent invention are described.

In this example, three kinds of substrates, that is, an SOI substrate Cmanufactured with the use of a glass substrate C subjected to HPMtreatment, an SOI substrate D manufactured with the use of a glasssubstrate D subjected to HPM treatment and ultrasonic cleaning and anSOI substrate E manufactured with the use of a glass substrate E whichis untreated were manufactured, and detection of the deficiency regionof a single crystal silicon film was performed with the use of adeficiency region detecting apparatus (a glass substrate surfacedetecting apparatus GI-4600 manufactured by Hitachi electronicengineering corporation). In the deficiency region detecting apparatus,a sample substrate is irradiated with a laser beam having a wavelengthof 780 nm and an output of 30 mW and then scattered light reflected atunevenness and light passing through the deficiency region are detectedby an optical receiver, whereby the number of the deficiency regions canbe counted. Scanning with a laser beam is performed in an X axisdirection and the sample substrate is moved together with a table in a Ydirection to scan a region of a single crystal silicon film having asize of 107 mm square, so that the deficiency regions of the singlecrystal silicon film are detected. Note that the deficiency regiondetecting apparatus used in this example recognizes the deficiencyregions of the single crystal silicon as severe recessed portions anddetects them. Therefore, since unevenness of a surface, dust and ablemish are also detected, evaluation and comparison need to beperformed with the results regarded as qualitative numerical values.

The samples used in this example are described. First, respective glasssubstrates used for the SOI substrates are described. The glasssubstrate C used for the SOI substrate C was subjected to the sametreatment as that of the glass substrate A in Example 1. In a process ofthe same treatment as the glass substrate A of Example 1, an ultrasonicoscillation bath in which a solution could be subjected to ultrasonicoscillation was filled with an HPM solution and the glass substrate Dused for the SOI substrate D was soaked in the cleaning bath filled withan HPM solution for 10 minutes while ultrasonic oscillation having afrequency of 37 kHz is applied thereto. Then, in a similar manner to theglass substrate A in Embodiment 1, the glass substrate was soaked in acleaning bath filled with pure water for 10 minutes and then dried witha rinser dryer, so that water droplets on the glass substrate wereremoved. In this manner, an altered layer was formed on each of surfacelayers of the glass substrate C and the glass substrate D. Further, theglass substrate E was left untreated. Note that each thickness of theglass substrate C, the glass substrate D and the glass substrate E is0.7 mm.

Next, bond substrates bonded to respective SOI substrates are described.First, a silicon oxynitride film was formed to have a thickness of 50 nmover a single crystal silicon substrate by a plasma CVD method. Inaddition, a silicon nitride oxide film was formed thereover to have athickness of 50 nm.

Next, the single crystal silicon substrate was irradiated with hydrogenthrough a surface of the silicon nitride oxide film by using anion-doping apparatus. In this embodiment, irradiation with ionizedhydrogen was performed to form an embrittlement layer in the singlecrystal silicon substrate. The ion doping was performed with anaccelerating voltage of 35 kV at a dose of 2.2×10¹⁶ ions/cm².

Next, a silicon oxide film was formed over the silicon nitride oxidefilm. The silicon oxide film was formed to have a thickness of 50 nm bya plasma CVD method using tetraethoxysilane (TEOS) (chemical formula:Si(OC₂H₅)₄) and an oxygen gas at a temperature of 300° C.

Then, each glass substrate and each bond substrate were subjected totreatment with ozone water and megasonic cleaning as surface treatment.After that, the glass substrates C, D and E are bonded to respectivesingle crystal silicon substrates with the silicon oxide film interposedtherebetween. Then, heat treatment was performed at 200° C. for 2 hoursand then at 600° C. for 2 hours, whereby a crack was formed in theembrittlement layer to separate the single crystal silicon substratefrom the glass substrate, and the bonding between the silicon oxide filmand the glass substrate was strengthened. In this manner, the glasssubstrates C, D and E were manufactured.

Results obtained by detecting deficiency regions of the single crystalsilicon film in each of the SOI substrates C, D and E are shown in FIG.18. In FIG. 18, based on the length of the deficiency region in adirection in which scan with a laser beam is performed, deficiencyregions in the SOI substrates are classified to S (longer than or equalto 1.0 μm and shorter than or equal to 3.0 μm), M (longer than or equalto 3.0 μm and shorter than or equal to 5.0 μm) and L (longer than orequal to 5.0 μm). Note that, as for the deficiency region, the length ina direction in which scan with a laser beam is performed is measured. Itis found that, as compared to the SOI substrate E in which the untreatedglass substrate is used, increase in the area and the number ofdeficiency regions is suppressed in the SOI substrate D in which theglass substrate subjected to HPM treatment is used. Further, as comparedto the SOI substrate C, increase of the size and the number ofdeficiency regions is suppressed in the SOI substrate D in which theglass substrate subjected to ultrasonic treatment in addition to HPMtreatment is used.

As described above, it was shown that formation of the altered layer onat least one surface of a glass substrate by HPM treatment suppressedincrease of the area and the number of the deficiency regions of thesingle crystal silicon film in the SOI substrate. In addition, it wasshown that increase of the area and the number of deficiency regions ofa single crystal silicon film in an SOI substrate was further suppressedby adding ultrasonic treatment to HPM treatment.

This application is based on Japanese Patent Application serial no.2008-178027 filed with Japan Patent Office on Jul. 8, 2008, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a substrate; afirst insulating layer over and in contact with the substrate; asemiconductor layer over the first insulating layer; a gate insulatinglayer over the semiconductor layer; and a gate electrode over the gateinsulating layer, wherein a thickness of the first insulating layer isgreater than or equal to 5 nm and less than or equal to 3 μm, andwherein the first insulating layer has a higher silicon oxide proportionand a lower density than the substrate.
 2. The semiconductor deviceaccording to claim 1, wherein the substrate is a glass substrate.
 3. Thesemiconductor device according to claim 1, wherein concentrations ofalkali metal and alkaline earth metal in the first insulating layer arelower than those in the substrate.
 4. The semiconductor device accordingto claim 1, wherein the semiconductor layer is a single crystalsemiconductor layer consisting essentially of silicon, germanium,silicon germanium, gallium arsenide, or indium phosphide.
 5. Thesemiconductor device according to claim 1, further comprising: a secondinsulating layer between the first insulating layer and thesemiconductor layer, wherein the second insulating layer is a singlelayer or a stacked layer selected from a group consisting of a siliconoxide film, a silicon nitride film, a silicon nitride oxide film, and/ora silicon oxynitride film.
 6. The semiconductor device according toclaim 1, wherein the semiconductor device is one of a computer, anRFCPU, a solar cell, a photo IC, and a semiconductor memory device.
 7. Asemiconductor device comprising: a substrate; a first insulating layerover the substrate; an intermediate layer between the substrate and thefirst insulating layer; a semiconductor layer over the first insulatinglayer; a gate insulating layer over the semiconductor layer; and a gateelectrode over the gate insulating layer, wherein a thickness of thefirst insulating layer is greater than or equal to 5 nm and less than orequal to 3 μm, wherein the first insulating layer has a higher siliconoxide proportion and a lower density than the substrate, and wherein theintermediate layer has intermediate values of a silicon oxide proportionand a density between values of the substrate and the first insulatinglayer.
 8. The semiconductor device according to claim 7, wherein thesubstrate is a glass substrate.
 9. The semiconductor device according toclaim 7, wherein concentrations of alkali metal and alkaline earth metalin the first insulating layer are lower than those in the substrate. 10.The semiconductor device according to claim 7, wherein the semiconductorlayer is a single crystal semiconductor layer consisting essentially ofsilicon, germanium, silicon germanium, gallium arsenide, or indiumphosphide.
 11. The semiconductor device according to claim 7, furthercomprising: a second insulating layer between the first insulating layerand the semiconductor layer, wherein the second insulating layer is asingle layer or a stacked layer selected from a group consisting of asilicon oxide film, a silicon nitride film, a silicon nitride oxidefilm, and/or a silicon oxynitride film.
 12. The semiconductor deviceaccording to claim 7, wherein the semiconductor device is one of acomputer, an RFCPU, a solar cell, a photo IC, and a semiconductor memorydevice.